The amyloid .beta.-protein precursor (APP) is a member of a highly conserved family of integral membrane glycoproteins, which currently includes APP and two APP-like proteins (APLP), APLP1 and APLP2 (Wasco, W. et al., Genomics 15:237-239 (1993); Wasco, W. et al., Nat. Genet. 5:95-100 (1993)). APP-like proteins have also been identified in mouse (Wasco, W. et al., Proc. Natl. Acad. Sci. U.S.A. 89:10758-10762 (1992); Slunt, H. et al., J. Biol. Chem. 269:2637-2644 (1994)), Drosophila (Rosen, D. et al., Proc. Natl. Acad. Sci. U.S.A. 86:2478-2482 (1989)), and C. elegans (Daigle, I. et al., Proc. Natl. Acad. Sci. U.S.A. 90:12045-12049 (1993)). However, only APP gives rise to the 4 kDa A.beta. peptide that aggregates in senile plaques and cerebral blood vessel deposits in the brains of patients with Alzheimer's disease (Masters, C. L. et al., EMBO J. 4:2757-2763 (1985); Glenner, G. G. et al., Biochem. Biophys. Res. Commun. 120:885-890 (1984)). The accumulation of the A.beta. peptide in amyloid plaques occurs in the brains of normal elderly individuals, to some extent, but is greatly enhanced in patients with Alzheimer's disease and Down's syndrome (Masters, C. L. et al., Proc. Natl. Acad. Sci. U.S.A. 82:4245-4249 (1985)). The presence of a third copy of the APP gene on chromosome 21 in Down's syndrome patients and the subsequent increased levels of APP mRNA (Tanzi, R. E. et al., Science 235:880-884 (1987); Rumble, B. et al., New Engl. J. Med. 320:1446-1452 (1989)) suggest that overexpression of the APP gene most likely leads to amyloid deposition in these individuals. Altered regulation of APP transcription could conceivably lead to a similar situation in localized areas of brains of Alzheimer's disease patients. Experiments with transgenic mice showed that APP overexpression indeed leads to amyloid deposition (Quon et al., Nature 352:239 (1991); Wirac et al., Science 252:323 (1991)).
Studies of the promoter region of the APP gene indicate that it lacks typical TATA and CAAT boxes and has multiple transcriptional start sites, characteristic of housekeeping genes (Salbaum, J. M. et al., EMBO J. 7:2807-2813 (1988)). It has been reported that one or more elements located between position -94 and -35 are responsible for an 8-fold increase in gene expression in HeLa cells (Pollwein, P. et al., Nucleic. Acids. Res. 20:63-68 (1992)). Studies of the mouse APP promoter have shown that two positive regulatory elements are located between positions -100 and -37, and that one of these elements binds the mouse Sp1 factor (Izumi, R. et al., Gene 112:189-195 (1992)). A "combined" element, in which the AP-4 site is followed by an overlapping AP-1 site (AP-1/AP-4 site) is situated approximately at position -45 and is completely conserved in the human, rat and mouse promoters (Izumi, R. et al., Gene 112:189-195 (1992); Chernak, J. M., Gene 133:255-260 (1993)). The deletion of the region containing the AP-1/AP-4 site in the rat APP promoter causes a 30 % decrease in transcriptional activity in PC-12 cells (Hoffman, P. W. et al., Biochem. Biophys. Res. Commun. 201:610-617 (1994)). Interestingly, it has been shown that APP mRNA levels change dramatically during differentiation of embryonic P19 cells induced with retinoic acid (Fukuchi, K. et al., J. Neurochem. 58:1863-1873 (1992)).
The presence of an unidentified factor interacting with the AP-1/AP-4 site of the APP gene has been reported in a variety of systems. In HeLa cells, it has been demonstrated that the Sp1 factor interacts with an upstream GC-rich region and competes for binding with a factor interacting with the AP-1/AP-4 site (Pollwein, P. et al., Nucleic. Acids. Res. 20:63-68 (1992); Pollwein, P., Biochem. Biophys. Res. Commun. 190:637-647 (1993)). The binding of an unknown factor to the region containing the conserved AP-1/AP-4 site in the rat APP promoter has been reported to occur in PC-11 cells and in rat brain (Hoffman, P. W. et al., Biochem. Biophys. Res. Commun. 201:610-617 (1994)). Finally, Quitshke et al. used a DNA fragment lacking the upstream GC-rich region and found that an unidentified factor binds to the AP-1/AP-4 site of the APP promoter in Y79 cells (Quitschke, W. W. et al., J. Biol. Chem. 267:17362-17368 (1992)). This factor did not appear to be related to the known AP-1 or AP-4 transcriptional factors. However, the identity of the factor(s) which binds to the AP-1/AP-4 site of the APP promoter has not yet appeared in the literature. The identification of factors involved in transcriptional regulation of the APP gene would provide critical clues regarding the events leading to the formation of amyloid deposits.